Chrome shows this info. When hovering over an item in the inspector, it is highlighted on the page, with its dimensions in a title text box. There is also a box diagram with dimensions in the right pane of the inspector, with the relevant CSS rules above it:
As for opening all levels automatically, I don’t know how to do this, but I’m sure there’s a setting that enables it. Someone else might know. Should note, however, that if you open the inspector by right clicking and choosing “Inspect Element”, the element in question will be expanded automatically.
